In a slim volume of his writings from prison, entitled Thoughts and published in 1991, Reggie Kray, who has died aged 66, concluded that "my eventual aim is to be recognised, first as a man and eventually as an author, poet and philosopher". He will certainly always be recognised, but only as one half of Britain's best-known team of gangsters, the leader of the Firm, a man who spent the first half of his life breaking the law and the second half paying for it.

Reggie and Ronnie Kray were born in London's East End, the twin sons of the feckless Charlie and the protective Violet. They came from Romany, Irish and Jewish stock, and their earliest aspirations to fame were in the boxing ring where, along with big brother Charlie, they excelled. But it soon became clear that their physical strength was going to be pressed into combat that took little notice of the Queensberry rules.

Their national service was spent mainly in the glasshouse for assaulting NCOs or going AWOL, and they emerged from Shepton Mallet military prison well prepared for a lifetime challenging authority.

By then, Ronnie - "The Colonel" - was already showing signs of the unbalanced personality that was to become both the strength and weakness of the twins: a strength in that Ronnie's sudden violent mood swings meant that other criminals and those who paid protection money were always fearful of him; a weakness, because it embroiled the three brothers in the pointless violence for which they eventually paid with more than 70 years of their collective lives behind bars.

It was in 1954 that the twins' reputation was established. They had taken over the Regal billiard hall on the Mile End Road, and Ronnie cutlassed members of a Maltese gang that tried to extract protection money from them. Word spread. They soon saw their future in clubs, either owning them, extracting protection money from them, or - in Ronnie's case - wielding them. By 1957, they had their own establishment, the Double R, in Bow Road, east London. The Firm, the name by which their gang was known, was born.

The Krays recruited a mixture of Scottish hardmen, London heavies and bent businessmen, and soon had a tight little empire in east London, within spitting distance of their old home (now demolished) on Vallance Road, "Fort Vallance" as it was called.

Had they been content with the regular earnings offered by people anxious to keep on their right side, they could have avoided the attention of what was, in the 1960s and early 70s, the often corrupt world of detectives happy to turn a blind eye. But they wanted to expand into the West End and this, coupled with Ronnie's increasing paranoia, derailed them.

Ronnie murdered fellow villain George Cornell by shooting him in the Blind Beggar pub, in the East End, in 1966. All the witnesses were, initially, too scared to give evidence against him, and, for a time, it seemed as though the Krays were untouchable. The following year, Reggie too crossed the line. According to one of their former henchmen, Albert Donoghue, Ronnie egged his brother on to kill Jack "The Hat" McVitie, a smalltime crook and irritant to the brothers. "I've done mine," Ronnie supposedly told Reggie. "About time you done yours."

McVitie was lured to a party in Hackney, where he was accused of damaging the Kray name, and stabbed to death by Reggie. Members of the Firm were left to clean up the mess while the body was disposed of.

Again, it looked initially as though the twins would get away with it, but Leonard "Nipper" Read, one of a new breed of clean Scotland Yard detectives, was determined to halt them. Reggie and Ronnie named one of their boa constrictors after Read when they heard he was on their trail, and he proved to be just as wily and powerful.

There turned out to be little honour among their gang of thieves and hard men: many gave evidence against the twins when they finally appeared at the Old Bailey in 1969. There they were jailed for life, with a recommendation that they serve at least 30 years.

If the sentencing judge, Mr Justice Melford Stevenson, hoped that the lengthy term would wipe the Kray name from the public mind, he was wrong. The twins became more famous with every year they spent in Broadmoor or Parkhurst. There was a Kray musical by Snoo Wilson (England, England), Kray t-shirts, The Krays film in 1990, Kray boxer shorts, more than 20 books (the best of which remains the earliest, John Pearson's The Profession of Violence) and, inevitably, a web site.

This constant attention may have stiffened the resolve of successive home secretaries to refuse to parole the twins, but the real reason was probably that Reggie continued to justify the McVitie killing - likening it to the slaying of an Argentinian soldier in battle.

Inside prison, Reggie kept himself fit, "adopted" a succession of young men, and wrote his memoirs and occasional poems. In Born Fighter (1990), he wrote that he had become a born-again Christian, and he stunned prisoners in Parkhurst by saying grace before Christmas dinner. His favourite reading, he said, was Kahlil Gibran's The Prophet. He also took up the metaphorical cudgels on behalf of gay prisoners who were bullied. In the past, he had helped other prisoners to escape (including, in the 1960s, "Mad Frank" Mitchell, later killed when he became a nuisance to the Krays, who were hiding him) but he never made it over the wall himself.

He gave interviews in jail, in which he was always the courteous gent, and campaigned for his freedom as his relatives gradually died. He was allowed out to attend the funerals of his mother and twin brother, who died in Broadmoor in 1995. Eventually, on August 26 this year, he was released on compassionate grounds, suffering from terminal cancer.

But even if he was much mocked - the generation of bank robbers who took over the criminal world referred to the twins as "Gert and Daisy", and Monty Python's Flying Circus lampooned them as the Piranha brothers - his following never disappeared. Young gangsters imitated and even named themselves after him and Ronnie, and there was never a shortage of people prepared to pay for the privilege of having their photo taken with him.

As a young man, Reggie had married Frances Shea in 1965, but she had committed suicide two years later, having left him. In the 1990s, through a friend, he met Roberta, a bright, attractive, public relations woman, who added her voice to calls for his release, visited him regularly, and became his second wife.

He argued that without the Kray name, he would have served a much smaller sentence - and he was right. The same aura of menace that had allowed the brothers such power in the old East End meant that their release was always going to attract attention, and it constantly delayed the chance for Reggie to re-enter a society he would barely have recognised, and a criminal world taken over by drugs.

Other families - the Richardsons, the Arifs, the Adams - may have emerged on the criminal scene, but none ever had the Kray cachet. Whether that was any consolation to Reggie is another matter. Ronnie had always wanted to be famous, to be a British Jimmy Cagney figure; Reggie might have been happier ending his days on the Costa del Sol, trying to work out exactly what philosophy it was that had made him so notorious.

 Reginald Kray, gang leader, born October 24 1933; died October 1 2000